Bob,
Unless you want to use a mirror format for the display, you have a couple of other things to think about. There are several threads on the forum on the very subject. Search for cameras, rear view cameras, etc. For just backing up any small bumper mount camera will do. What is displayed is "usually" good enough to get into a parking space. I think you will not be that happy with the unit you are looking at. The CMOS cameras will give you a slightly greenish hue to the picture. You want to look for CCD units to get better image. The display is not going to be that important for just backing up. If you want to use the camera to really look back as a mirror would do, then you have to start thinking where you are going to mount the camera. Much higher than where a bumper would be. Other wise you will be looking at the road and you won't be able to judge anything coming up on you. You would also have to start thinking about Field Of View. anything more than 90 degrees will make all images approaching very small until they are right up on you, then they will look very big. Several of the SLC guys have set theirs up with their tablets and use usb cameras and they look really good. Problem is they take up too much room for A 40. GOOGLE rear view cameras and you will get several sites that can handle pretty much what you want. There are cameras out there that are recorders as well and look in both directions(front and rear)
I have a 3 cameras setup on my 40 that handles all rear functions. One was mounted up on the top rear section of the spyder, but it has been removed for the time being as it looked like, as one forum member said, like a wart up there. It will be replaced with a tiny ball type camera The other two are hidden inside my side mirrors, and I use a screen(7") that displays all the cameras at once or sequentially.My screen is mounted slightly under the dash, in the center and aimed toward the drivers seat. It isn't distracting at all. I got them years ago before there were usb cameras, and are CMOS units with 120 degree FOV. The way they function is really good for me. I am able to judge overtaking cars fairly well. As the approaching car leaves the center mirror(the one I just removed), it comes into the side mirror. As it leaves that mirror it is at my window and I can see them there.
One other point, some of the screens that are employed today are rather bright and that may hamper you in a backing situation(at night). My F150(2013) almost blinds me when backing at night and I am not able to see very well with my regular mirrors. The fish eye lens employed lets me see the side areas but I can't judge how far away they are. Directly behind me has a warning bar and beeper.
You may want to go to some of the dealers to "test drive" their units to see if that is what you really want. FYI the older threads have some good info on them even though they are dated.
Bill